HI, I'm new to the world of NSR's (and 2strokes come to that!).

I've just purchased an MC21, a bit tatty (has anyone a top fairing spare?), but run's well and the frame etc is straight.

After an initial check over, new plug's (had B8ea fitted!!!), new chain,front tyre and rear wheel bearing's, everything else seem's fine.

Little else is known about the bike or if anyone has attempted to tune the motor.
Twin carbon end pipes both exit on the right of the bike, (make unknown).

A compression check showed both cylinder's to be about 140psi.

My first "proper" ride was a love / hate affair.

The bike run's sweet through the low midrange (upto about 6K), but from 6500rpm to 8500rpm the motor feel's strangled, flat, not misfiring but a kind of 'stutter'. This characteristic is worse in higher gear's and/or going uphill ie under greater engine load.

As soon as the powervalve move's at 8500rpm the exhaust note change's and the bike takes off instantly and again rev's cleanly and smoothly upto (and into - oop's) the red line.

I believe the valve should switch at about 6500rpm, is this right?

Does anyone have any advice / opinion's on what might be wrong?

My first port of call will be to check the powervalve cable's adjustment.

I will then check to see if the bike has been derestricted. (there's no black box)

Is there anyway to reduce (or check) the rpm at which the valve alter's, as this appear's to be the problem, would a late opening valve cause this type of running alone?


Any help much appreciated!

regard's Phil

N. York's

'01 TRX 850
'76 400/4
'93 NSR 250 MC21

Hi Phil,

Welcome to the best bike on the planet!

Surf over to www.tygaperformance.com for a replacement fairing. Be prepared to empty your wallet into their coffers - they've some very cool NSR gear.

What year is the bike? And do you know which MC21 it is? The R is pretty basic, the SE has twiddly bits on the suspension, the SP has that, a dry clutch and magnesium alloy wheels.

140psi is an excellent compression figure, so it sounds like someone did a rebuild in the not too distant past.

To be honest, the engine behavior doesn't sound too odd to me. All two strokes are a bit 'female' as the power valve does it's thing. What colour are the spark plugs? It may be that you need to alter the jetting a bit to get the mid-range sorted, so the first thing is to get the main jet set right, then start mucking about with needles.
_________________
MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

Hi and thanx for the reply.

The bike is a '93 MC21, 250R7L, so it's just the basic spec.

As the bike was cheapish (£400), I didn't fancy splashing out on a new fairing, guess I'll keep an eye on the classified's!!!

I've drained the oil (unknown quality) and replaced with fully synthetic Motul, the power valves are now correctly adjusted.

As for being restricted, the orange/blue wire has been cut and taped back but not connected to anything else, while I am not interested in top speed, what effect would this have?

The GPS wires are in standard form.

If the ignition (derestriction) mod is carried out as outlined in NSR WORLD, does it increase top speed AND horsepower?
If so are any other mod's required (ie carb) to keep thing's sweet.

Thanx for a fab site,
Sorry about the question's I'm on a steep learning curve at the moment, and want the bike running as sweet as possible.

Regard's Phil